As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of secondary batteries has also sharply increased. Among them is a lithium secondary battery having high energy density and operating voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as the mobile devices.
On the other hand, various kinds of combustible materials are contained in the lithium secondary battery. As a result, the lithium secondary battery may be heated or explode due to the overcharge of the battery, the overcurrent in the battery, or other physical external impacts. That is, the safety of the lithium secondary battery is very low. Consequently, a positive temperature coefficient (PTC) element and a protection circuit module (PCM), as safety elements for effectively controlling an abnormal state of the battery, such as the overcharge or the overcurrent of the battery are connected to the lithium secondary battery.
Generally, the PCM is connected to the battery cell via conductive nickel plates by welding or soldering. That is, the nickel plates are connected to electrode tabs of the PCM by welding or soldering, and then the nickel plates are connected to electrode terminals of the battery cell by welding or soldering. In this way, the PCM is connected to the battery cell to manufacture a battery pack.
It is required for the safety elements, including the PCM, to be maintained in electrical connection with the electrode terminals of the battery cell and, at the same time, to be electrically isolated from other parts of the battery cell. Consequently, a plurality of insulative mounting members or parts are required to construct such connection, which complicates the battery assembly process, and reduces a space for receiving the battery cell.
Also, a large number of welding or soldering processes are required to construct the battery pack, and the welding or soldering processes must be carried out with high precision because of the small structure of the secondary battery. As a result, a defect possibility is great. Furthermore, the welding or soldering processes are added during the manufacturing process of a product, which increases the manufacturing costs.
Consequently, research has been actively made on a technology for reducing the number of parts loaded on the top of the battery cell and increasing the capacity of the battery cell. For example, Korean Patent Application Publication No. 2005-0121116 discloses a secondary battery having a protection circuit unit coupled to the outer surface of a bare cell, wherein the protection circuit unit is configured in the shape of an assembly made of molding resin, connection terminals are formed at the interface between the protection circuit unit and the outer surface of the bare cell for coupling the protection circuit unit and the bare cell, and the protection circuit unit is provided with a space for exposing a contact region between the protection circuit unit and the connection terminals of the bare cell where the protection circuit unit and the connection terminals of the bare cell are to be welded such that the welding is easily carried out.
In the above-described conventional technology, however, it is required to form the space for exposing the region to be welded to the outside between the bare cell and the protection circuit unit. As a result, the overall volume of the battery pack increases, and therefore, the space for receiving the battery cell decreases.
Also, Korean Patent Application Publication No. 2006-0101573 discloses a battery protection circuit board having battery cell connection terminals, wherein a lead-type static characteristic poly switch is directly connected to one of the battery cell connection terminals on the battery protection circuit board by soldering such that the lead-type static characteristic poly switch is mounted on the surface of the battery protection circuit board.
However, the disclosed battery protection circuit board is manufactured by a series of complicated processes including a process of manufacturing a printed circuit board (PCB), a process of applying paste-type solder to the manufactured PCB and mounting parts constituting a protection circuit, including the static characteristic poly switch, on a predetermined position of the PCB using a mounting apparatus, a reflow process, a process of heat-treating the protection circuit board passing through the reflow process, and a process of inspecting the protection circuit board including the lead-type static characteristic poly switch. Consequently, the process of manufacturing the battery is complicated, and therefore, the productivity is lowered.
Consequently, there is a high necessity for a technology that is capable of reducing the number of members mounted to the top of the battery cell to simplify the assembly process, reducing the number of welding processes to decrease a defect rate, achieving stable coupling between the members loaded on the top of the battery cell, and increasing the capacity of the battery cell while solving the above-mentioned problems caused in the conventional art.